An image forming apparatus, such as a copying machine, a printer, a facsimile machine, a plotter, or a multifunction printer having copying, printing, scanning, and facsimile functions, can form an image on a recording medium (e.g., a sheet) by a liquid discharging method. For example, a recording head (e.g., a liquid discharging head) discharges a recording liquid (e.g. an ink drop) onto a conveyed sheet to form an image on the sheet. Alternatively, an image forming apparatus can form an image on a sheet by an electrophotographic method.
In the image forming apparatus using the liquid discharging method, the recording head is requested to discharge an ink drop onto a sheet with an increased precision so as to form a high-quality image. To cope with this request, the image forming apparatus includes a belt conveying device for conveying a sheet. In the belt conveying device, a surface of a conveying belt is uniformly charged by generating a direct or alternating current electric field. An electrostatic force on the conveying belt attracts a sheet. A constant gap is provided between the recording head and the sheet on the conveying belt. Feeding of the sheet is controlled to prevent the sheet from being skewed and levitated. Thus, the sheet does not hit the recording head and thereby is not jammed and stained. Alternatively, the conveying belt may attract a sheet by air.
The belt conveying device further includes a driving roller and a driven roller (e.g., a tension roller). The conveying belt has an endless belt shape and is looped over the driving roller and one or more driven rollers. The conveying belt rotates to convey a sheet.
When the conveying belt moves obliquely, the conveying belt may not stably convey a sheet. When the conveying belt is installed in an image forming apparatus using the liquid discharging method, ink drops discharged by the recording head may impact various positions on a sheet. As a result, the image forming apparatus may not stably form a high-quality image. To cope with this problem, a bead for regulating the conveying belt is provided on an inner circumferential surface of the conveying belt.
One example of a background image forming apparatus includes an engine unit including an image forming member (e.g., a recording head), a carriage, a scanning mechanism, and a belt conveying device. The recording head is mounted on the carriage and discharges an ink drop to form an image on a sheet. The scanning mechanism moves the carriage in a main scanning direction. The belt conveying device conveys a sheet in a sub-scanning direction. The engine unit is attachable to and detachable from the image forming apparatus. The belt conveying device includes a frame and a belt unit including a conveying belt, a driving roller, and a driven roller. The conveying belt has an endless belt shape and is looped over the driving roller and the driven roller. The frame supports the belt unit. Namely, when the belt unit is set on the frame, the belt unit is properly positioned in the engine unit.
However, when the frame is warped or deformed, the belt unit may not be properly positioned in the engine unit. For example, the driving roller and the driven roller are not positioned in parallel to each other. As a result, the conveying belt may move obliquely or may be mounted on the frame.
In the belt unit, one end of each of the driving roller and the driven roller in an axial direction of the driving roller and the driven roller may be supported by a common support. However, another end of each of the driving roller and the driven roller in the axial direction of the driving roller and the driven roller needs to be supported by another support, because the endless conveying belt may not be looped over the driving roller and the driven roller when one common support supports both ends of the driving roller and the driven roller in the axial direction of the driving roller and the driven roller. As a result, another end of each of the driving roller and the driven roller may easily deviate upward or downward relative to one end of each of the driving roller and the driven roller. Namely, the driving roller and the driven roller are not positioned in parallel to each other. Thus, the conveying belt may move obliquely or may be mounted on the frame.